The present invention relates generally to roof bolt machines that are employed in coal mines to install roof bolts that support the roof of the mine. More particularly the present invention relates to a quartz trapping device that is adapted to operatively attach to an exhaust of a dust system circuit of a roof bolt machine to reduce or substantially eliminate the amount of respirable dust and respirable quartz dust that is released to the working environment. The invention also relates to an improved roof bolt machine comprising said quartz trapping device and a method for reducing or substantially eliminating emissions of respirable dust and respirable quartz dust into the working environment from the exhaust stream of roof bolt machines.
When a mine tunnel is cut into the earth, the material forming the roof of the mine is relatively weak and will tend to collapse unless it is supported. The roof of a mine has been supported by drilling holes in the roof of the mine and inserting bolts into the holes. Typically, the upper end of each bolt is anchored in a hole and the bolt is tightened against a mine roof support plate to compress the material forming the mine roof.
Special machines known generally as roof bolt machines have been developed for assisting in the roof drilling and bolting process. Roof bolt machines are described, for instance, in U.S. Pat. Nos. 3,252,525; 3,337,880; 3,768,574; 3,842,610; 3,951,215; 4,050,259; 4,079,792; 4,290,490; 4,294,317; and 4,589,803 and which are incorporated herein by reference to the extent that is not inconsistent with the disclosure and claims of the present application. A typical roof bolt machine comprises a mobile chassis, including at least an operator""s platform or a cab. A drilling assembly is mounted on the mobile chassis and includes a drillhead that has a drill bit that is operable to drill holes in a mine roof.
Large amounts of respirable dust and especially respirable quartz dust also known as respirable silica are released into the environment in coal mines through the dust exhaust stream of roof bolt machines, especially when the roof bolt machines are used to drill holes in a sandstone roof. The term xe2x80x9crespirablexe2x80x9d refers to very small size dust and quartz particles, which when present in the air, are inhaled by humans and are deposited in the lungs. Generally, respirable dust or quartz dust particles have an average size of less than about 5 microns. Overexposure to respirable quartz found in dust can cause scar tissue to form in the lungs, reducing the ability of the lungs to extract oxygen from the air we breathe, a disease known as silicosis. Silicosis is incurable but it can be prevented by implementing engineering controls in the work place that minimize the exposure of workers to respirable quartz dust. Because of the significant health risks associated with breathing respirable quartz dust found in the dust generated during drilling operations, mine operators take measures to reduce dust emissions into the working environment. For instance existing roof bolt machines employ a dust system circuit that includes a vacuum source, such as a blower, that creates a vacuum which is applied through connecting hoses to the drillhead unit of the roof bolt machine. The vacuum draws the drill cuttings and dust that are generated during drilling operation into a dust collection system before releasing the dust exhaust stream from the outlet of the vacuum source into the working environment. Existing dust collection systems employed by roof bolt machines are generally expensive, cumbersome, ineffective in removing very small size quartz particles, difficult to maintain and often times clog and result in a loss of production. Existing dust collection systems typically require that filters capable of trapping very fine particles, e.g., less than 15 microns in size, be used to remove the respirable size dust and quartz dust. These filters are expensive, not always very effective in capturing the very small size respirable dust, require regular maintenance and tend to clog rather easily, thus disrupting operations.
Therefore, there exists a need for an improved roof bolt machine that has a quartz trapping device that is economical, easy to maintain and effective in reducing the amount of respirable dust, especially respirable quartz dust, that is released into the environment during drilling operations.
The present invention provides an improved roof bolt machine that includes a quartz trapping device that is economical, easy to maintain and effective in reducing the amount of respirable dust, and respirable quartz dust, that is released into the environment.
In its broadest aspects the quartz trapping device of the present invention, which is also referred to as a quartz trapping apparatus or a quartz zapper, comprises a container partially or at least partially filled with a liquid. The container includes a top plate, a bottom plate and side plates. The container comprises at least one inlet that is adapted to be operatively attached to the dust system circuit of a roof bolt machine for introducing the dust exhaust stream from the roof bolt machine, particularly from a dust system circuit of the roof bolt machine, that contains respirable dust and respirable quartz dust inside (or into) the container. The container comprises a plurality of baffles, extending downward from the top plate, and a plurality of baffles extending upward from the bottom plate. The downward and upward extending baffles are arranged in an alternating configuration. The baffles, together with the liquid, form a tortuous path through which the dust exhaust stream is conducted in order to contact the liquid, to cause the respirable dust and respirable quartz dust to be captured by the quartz trapping device, and particularly by the liquid, and form a substantially clean exhaust stream leaving the quartz trapping device. The dust exhaust stream is contacted with the liquid inside the quartz trapping device repeatedly a number of times sufficient to remove at least a significant amount and preferably substantially all of the respirable dust and respirable quartz dust found in the dust exhaust stream. The container further includes an outlet for releasing the substantially clean exhaust stream into the environment.
The quartz trapping device may be used in conjunction with any dust collection devices or systems employed in roof bolt machines.
One embodiment of the present invention is directed to a roof bolt machine comprising a mobile chassis, at least one operator cab operatively connected to the mobile chassis, at least one drilling assembly mounted on the mobile chassis and operatively connected with said mobile chassis mounted on the drillhead. The drilling assembly comprises a drillhead including a drill bit. A motor is mounted on the mobile chassis, and is operatively connected to the drillhead for turning the drill bit. The roof bolt machine further comprises a dust system circuit comprising a vacuum source, a dust collection device (also referred to herein as a xe2x80x9cdust collection systemxe2x80x9d), and at least one connecting hose for operatively connecting the drill bit with the vacuum source and the dust collection device, for applying a vacuum to the drill bit sufficient to draw drill cuttings and dust generated during the operation of the drill bit through the dust collection device. The roof bolt machine of the present invention further comprises a quartz trapping device which is preferably mounted downstream of the vacuum source of the dust system circuit or downstream of a muffler, which may also be included in the dust system circuit, downstream of the vacuum source.
The present invention further relates to a method for reducing respirable dust and respirable quartz dust, from the exhaust of a roof bolt machine, particularly from a dust system circuit of a roof bolt machine. The method comprises, introducing the exhaust stream from the dust system circuit into the quartz trapping device of the invention, directing the exhaust stream through the tortuous path formed by the plurality of baffles of the quartz trapping device to contact the liquid under conditions effective to remove a substantial amount of respirable dust and respirable quartz from the exhaust stream to form a substantially clean exhaust stream which is substantially free of respirable dust and respirable quartz and releasing the substantially clean exhaust stream through an outlet. The quartz trapping device is preferably placed downstream of the vacuum source of the roof bolt machine.